Capacitive magnetic field sensor

ABSTRACT

The invention relates to a capacitive magnetic field sensor. This sensor has a first electrode ( 2 ) and a second electrode ( 3 ), which are spaced apart from one another and which form a measurement capacitance. The first electrode ( 2 ) is situated on a first substrate body ( 4 ), and the second electrode ( 3 ) on a second substrate body ( 5 ). The second substrate body ( 5 ) is designed as a deformable membrane in the vicinity of the second electrode ( 3 ). A magnetic body ( 6 ) is situated in the vicinity of the second electrode ( 3 ) and the membrane, and is rigidly connected to the membrane and to the second electrode ( 3 ). As a result of this rigid connection, the influence of an external magnetic field on the magnetic body causes not only the magnetic body ( 6 ) to change its position but also causes the membrane and the second electrode ( 3 ) to change their position, since they are rigidly connected to said magnetic body. Because the second electrode ( 3 ) changes its position, its distance from the first electrode ( 2 ) changes, and thus the measurement capacitance, which acts as a measure of the externally applied magnetic field. This capacitive magnetic field sensor is distinguished by very small exterior dimensions, great mechanical stability, and low temperature dependence.

BACKGROUND OF THE INVENTION

The present invention relates to the field of magnetic field sensors,and in particular to the field of capacitive magnetic field sensors.

Magnetic field sensors are often based on the Hall or magnetoresistiveeffect. These magnetic field sensors are extremely temperaturedependent, and as a result they are not well suited for high-precisionapplications or else require expensive electronic or electricaltemperature corrections.

Capacitive sensors are customarily used for measuring poses oraccelerations. These generally prove to be mechanically very stable andhave small exterior dimensions.

There is a need for a magnetic field sensor which depends less oninterfering temperature effects.

SUMMARY OF THE INVENTION

A capacitive magnetic field sensor includes two electrodes, which arespaced apart from one another and which form a measurement capacitance.The first electrode is situated on a first substrate body, and thesecond electrode on a second substrate body. The second substrate bodyis designed as a deformable membrane in the vicinity of the secondelectrode, and has a magnetic body, which is rigidly connected to themembrane and to the second electrode. If the magnetic body is caused tochange its position by an external magnetic field, this change ofposition is imparted to the membrane and to the second electrode throughthe rigid connection between the magnetic body, the membrane, and thissecond electrode. The distance between the two electrodes is thuschanged, so that the measurement capacitance of the sensor changes as afunction of the external magnetic field. This yields a reliablemeasurement of the magnetic field strength through the change of thecapacitive properties of the sensor.

This type of structure of the magnetic field sensor signficantly reducesits temperature dependence, since the elastic properties of thecapacitive sensor are much less subject to temperature dependencies thanthe prior art sensors based on the Hall or magnetoresistive effect.Furthermore, the inventive capacitive magnetic field sensor proves to bemechanically very stable, not prone to trouble, and also has smallexternal dimensions.

It proves to be especially advantageous to situate the second electrodeand the magnetic body on different sides of the membrane. This excludesa mechanical or electrical direct effect of the magnetic body throughthe second electode due to the membrane which separates them. Thisarrangement also proves to facilitate manufacturability of the sensor,since the two sides of the membrane can be subjected to differentproduction processes, which cannot mutually influence or disturb oneanother through their mechanical separation by the membrane. Theproduction process for the capacitive magnetic field sensor is thussimplified and made economical.

The magnetic body can be constructed as a thin, flat layer, whosesurface is joined to the membrane. This surface connection produces avery rigid arrangement of a layer-like magnetic body, the membrane, andthe second electrode. This rigid structure of the various materialsreduces the mechanical temperature depondence of the properties of thecapacitive sensor.

Furthermore, this layer can be applied easily in the manner of anelectrochemical deposition process, comparable to the process forapplying printed circuits to circuit boards. This makes it possible toproduce a layer with a defined thickness, and assures that a definedquantity of magnetic material is used for the magnetic body, a quantitywhich is sufficient to influence the position of the magnetic bodyadequately through the action of an external magnetic field and thus todetermine the magnetic field strength. The use of ferromagnetic materialhas proven to be especially beneficial. Such material can be appliedsimply and securely by appropriately designing the deposition method.

According to a preferred embodiment of the capacitive magnetic fieldsensor, an electronic arrangement for processing the measurement signalsis integrated into at least one of the substrate bodies. Thisintegration takes the form of an integrated circuit. This assures that,in addition to the compact structure of the capacitive sensor, anelectronic arrangement for evaluating the measurement signals is alsopresent, which is characterized by low loss power in the path from theactual capacitive magnetic field sensor to the arrangement forprocessing the measurement signals and an especially goodsignal-to-noise ratio, and thus provides a differentiated evaluation andrepresentation of the magnetic field strength. The capacitive magneticfield sensor thus proves to be a compact and reliable magnetic fieldsensor with high resolution. Such sensors are especially important inthe automobile industry, where limited space is generally available.

The electronic arrangement for processing the measurement signal ispreferably situated in the first substrate body below the electrode thatis affixed thereto. This structure in the mechanically rigid, immobilefirst substrate body also assures a mechanically trouble-free electronicarrangement for processing the measurement signals. This significantlyextends the field of application of this capacitive magnetic fieldsensor, and makes it especially suitable for the automobile industry orthe aircraft industry.

It is especially advantageous to divide the electronic arrangement forprocessing the measurement signals and to situate the parts separatelyin the two different substrate bodies. Here, too, the electronicarrangement is preferably designed in the manner of an integratedcircuit. Through this division, electronic functional groups such asamplifiers, evaluation units, or control units can be electronicallydecoupled from one another, and thus cross talk from one functionalgroup to the other functional group can be prevented. Precisely in thecase of very weak signals with especially poor signal-to-noise ratio,very accurate measurement results for the field strength neverthelesscan be calculated and displayed, since now this arrangement forprocessing the measurement signals markedly reduces any impairment ofthe measurement results due to cross talk between amplification,evaluation, etc.

It has proven especially suitable to design the capacitive magneticfield sensor so that at least one of the electrodes is formed byconductor tracks on the respective substrate, which are preferably partof the electronic arrangement for processing the measurement signals.Through this design, the electrodes can be produced rather simply, andtheir form and dimension can be specifically adapted to the particularrequirements. This yields a compact, reliable, and high-resolutioncapacitive magnetic field sensor. When the conductor track of theelectronic arrangement is used both as an electrode and as an electronicelement, it becomes possible to achieve a high degree of integration forthe overall arrangement and to use this conductor track synergetically.

An especially advantageous capacitive magnetic field sensor has anelectrode whose spatial structure makes it able to provide still morespatial resolution of the arrangement of the electrodes relative to oneanother, beyond their pure distance from one another. This makes itpossible to show and make available to the user not only the puremagnetic field strength but also the orientation of the magnetic fieldor the time- or space-change of the magnetic field, by a space-resolvingmeasurement. This aspect comes to bear when the two electrodes are notdisposed parallel to one another through an external influence, e.g.,the pattern of the magnetic field or the time- or space-change of themagnetic field, but rather are situated at an angle to one another andthis angle changes through the flexible design of the membrane and/orthe motion of the electrodes relative to one another. Such changes proveuseful to the user of the capacitive magnetic field sensor, since heobtains additional information about the time or space behavior of theexternal magnetic field. Such information allows conclusions regardingthe further actuation and/or amplification of the measurement signals.It has proven advantageous to dispose the electronic arrangement for thespace-resolving processing of the measurement signals of the spatiallystructure electrode of the electronic arrangement for processing themeasurement signals in one or in both substrates. Here, too, thisarrangement proves to be especially advantageous both in terms ofproduction engineering and as regards the compactness of the capacitivemagnetic field sensor as well as regards its mechanical stability.

Although the present invention has been shown and described with respectto several preferred embodiments thereof, various changes, omissions andadditions to the form and detail thereof, may be made therein, withoutdeparting from the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross sectional illustration of a capacitive magnetic fieldsensor; and

FIG. 2 is a more detailed cross sectional illustration of a capacitivemagnetic field sensor.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically illustrates a capacitive magnetic field sensor 1.The capacitive magnetic field sensor 1 includes a first electrode 2,which is situated on a first substrate body 4. A second electrode 3 isassociated with the first electrode 2, and is situated at a distancetherefrom. It is affixed to a second substrate body 5. The secondsubstrate body 5 is designed as a membrane in the vicinity of the secondelectrode 3. In this way, the distance between the two electrodes 2 and3 can change under the action of a force on the membrane, more or lessdepending on the type and hardness of the membrane. In this capacitivemagnetic field sensor, a magnetic body 6 is situated on the backside ofthe membrane, that is on the side which faces away from the secondelectrode 3. Depending on an external magnetic field, said magnetic bodyapplies a defined force on the membrane, and thus moves the membranetogether with the second electrode 3, thereby changing the distancebetween the two electrodes 2 and 3. This change of distance causes achange in the capacitance of the arrangement consisting of the twoelectrodes 2 and 3. This change of capacitance is amplified andevaluated by an arrangement (not shown) for processing the measurementsignals in the first substrate 4. The capacitive magnetic field sensor 1thus makes it possible to reliably measure the field strength of theexternal magnetic field, without strong temperature dependencies.

FIG. 2 is a cross sectional illustration of a capacitive magnetic fieldsensor 10. The sensor illustrated in FIG. 2 is substantially the same asthe sensor illustrated in FIG. 1, with the principal exception that thesensor 10 illustrated in FIG. 2 illustrates electronic arrangement 12for processing the measurement signals.

Although the present invention has been shown and described with respectto several preferred embodiments thereof, various changes, omissions andadditions to the form and detail thereof, may be made therein, withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A capacitive sensor with a first electrode and asecond electrode, which are spaced apart from one another and which forma measurement capacitance, such that the first electrode is situated ona first substrate body and the second electrode on a second substratebody, and the second substrate body is designed as a deformable membranein the vicinity of the second electrode, characterized in that amagnetic body is disposed in the vicinity of the second electrode andthe membrane, which magnetic body is connected to the membrane and tothe second electrode in such a way that a change of position of themagnetic body, induced by an external magnetic field, will cause achange of position of the second electode via the membrane, resulting ina capacitance change, wherein sand capacitive sensor further comprisesan electronic arrangement situated in the first substrate body below thefirst electrode affixed thereon for processing the measurements signals.2. The capacitive sensor of claim 1, wherein the second electrode andthe magnetic body are situated on opposite sides of the membrane.
 3. Thecapacitive sensor of claim 2, wherein the magnetic body is formed as athin layer.
 4. The capacitive sensor of claim 3, wherein the magneticbody contains ferromagnetic material.
 5. The capacitive sensor of claim1, wherein a first part of the electronic arrangement for processing themeasurement signals is situated in the first substrate body and a secondpart of the electronic arrangement for processing the measurementsignals is situated in the second substrate body.
 6. The capacitivesensor of claim 1, wherein the electronic arrangement for processing themeasurement signals has elements to amplify the measurement signal. 7.The capacitive sensor of claim 1, wherein the electronic arrangement forprocessing the measurement signals has elements for applying a voltagesignal across the first and second electrodes.
 8. The capacitive sensorof claim 1, wherein at least one of the electrodes is formed as at leastone conductor track.
 9. The capacitive sensor of claim 8, wherein theconductor track is part of the electronic arrangement for processing themeasurement signals.
 10. The capacitive sensor claim 9, wherein thefirst electrode is configured and arranged with respect to the secondelectrode to provide a space-resolving measurement.
 11. The capacitivesensor of claim 10, wherein the first electrode has mutually parallel,strip-shaped elements.
 12. The capacitive sensor of claim 11, whereinthe electronic arrangement for processing the measurement signalsprocesses the measurement signals to provide the space-resolvingmeasurement.